FIG. 25 is a block diagram of a conventional color conversion method and a color conversion device, as disclosed for example in Japanese Unexamined Patent Publication No. 6-86059 and referred to herein as "conventional example 1."
In FIG. 25, R1 denotes an input .gamma.-correction part which performs .gamma.-correction of R, G and B signals read by a scanner part, R2 denotes a pre-processing part which generates the minimum signal L by judging the magnitude of the .gamma.-corrected R, G and B signals, generates the differential signals X,Y between the input R, G and B signals and the minimum signal L, and generates the region selection signal S, R3 denotes a color conversion parameter memory part which accumulates the color conversion parameter with the region selection signal S as the address, R4 denotes an achromatic output signal generation part which generates the output signal P.sub.1 corresponding to the achromatic input based on the minimum signal L, R5 denotes an interpolation operating part which generates the output P.sub.2 by interpolating the space to be formed by the minimum signal L and the differential signals X,Y by the triangular prismatic interpolation, R6 denotes a limit processing part which performs the limit processing by adding the outputs P.sub.1, P.sub.2, R7 denotes an output .gamma.-correction part which prepares the output signal P through .gamma.-correction of the limit-processed signal P.sub.3, and the output signals P generated by the output .gamma.-correction part R7 are the ink quantity control signal of Y (yellow), M (magenta), C (cyan), etc., and supplied to the printer part after gradation processing in a systematic dither method by a dither processing part.
Conventional example 1 having the above-mentioned constitution is further explained as follows. The input .gamma.-correction part R1 performs .gamma.-correction of the signal read by a scanner part with linear reflectance using a look-up table method of R=G=B for the achromatic input. The pre-processing part R2 judges the magnitude of R, G and B signals based on the input R, G and B signals, sets the region selection signal S, and generates the minimum signal L and the differential signals X,Y between the minimum signal L and the input R, G and B signals.
The differential signals are determined as follows.
if ((R.gtoreq.G) & (G.gtoreq.B)), S=0, L=B, X=R-L, Y=G-L PA1 if ((G&gt;R) & (R.gtoreq.B)), S=1, L=B, X=G-L, Y=R-L PA1 if ((G.gtoreq.B) & (B&gt;R)), S=2, L=R, X=G-L, Y=B-L PA1 if ((B&gt;G) & (G&gt;R)), S=3, L=R, X=B-L, Y=G-L PA1 if ((B&gt;R) & (R.gtoreq.G)), S=4, L=G, X=B-L, Y=R-L PA1 if ((R.gtoreq.B) & (B&gt;G)), S=5, L=G, X=R-L, Y=B-L PA1 if (P.sub.1 +P.sub.2 &gt;255), P.sub.3 =255 PA1 if (P.sub.1 +P.sub.2 &gt;0), P.sub.3 =0 PA1 else P.sub.3 =P.sub.1 +P.sub.2 PA1 h.sub.11 &lt;1.0 Decrease the saturation of C.sub.1. PA1 h.sub.11 &gt;1.0 Increase the saturation of C.sub.1. PA1 h.sub.21 &lt;0 C.sub.1 -hue in f-axis direction PA1 h.sub.21 &gt;0 C.sub.1 +hue in f-axis direction PA1 h.sub.31 &lt;0 Decrease the brightness of C.sub.1. PA1 h.sub.31 &gt;0 Increase the brightness of C.sub.1. PA1 h.sub.12 &lt;0 C.sub.2 -hue in S-axis direction PA1 h.sub.12 &gt;0 C.sub.2 +hue in S-axis direction PA1 h.sub.22 &lt;1.0 Decrease the saturation of C.sub.2. PA1 h.sub.22 &gt;1.0 Increase the brightness of C.sub.1. PA1 h.sub.32 &lt;0 Increase the brightness of C.sub.2. PA1 h.sub.32 &gt;0 Increase the brightness of C.sub.2.
The color conversion parameter memory part R3 is a memory with the region selection signal S as the address input, and four color conversion parameters a.sub.s0, a.sub.s1, a.sub.s2 and a.sub.s3 set for each below-mentioned unit triangular prism are accumulated as a set. The achromatic signal generation part R4 outputs P.sub.1 =R(=G=B) when R=G=B. The achromatic signal generation part R4 comprises a through circuit where P.sub.1 =L. The interpolation operating part R5 obtains the output P.sub.2 by performing interpolation of the triangular prism based on the minimum signal L and the differential signals X,Y from the pre-processing part R2 and the color conversion parameters a.sub.si read from the color conversion parameter memory part R3.
Where the output value set at the apex (lattice point) of the triangular prism is T.sub.i (T.sub.0, T.sub.1, T.sub.2, T.sub.3), the output value P.sub.2 in the coordinate (L, X, Y) in the unit triangular prism is calculated by the following formula, where the lattice point value on the L-axis (X=0, Y=0) is zero, and L, X and Y are assumed to be normalized to 0.about.1. EQU P.sub.2 =T.sub.0.multidot.X+(T.sub.2 -T.sub.0).multidot.L.multidot.X+T.sub.1.multidot.Y+(T.sub.3 -T.sub.1).multidot.L.multidot.Y
The limit processing part R6 adds the output value P.sub.1 to the output value P.sub.2, and outputs the output value P.sub.3 through the over-flow and under-flow processing. That means,
The output .gamma.-correction part R7 performs .gamma.-correction so that the reflection is linear during printing to the linear reflection signal P.sub.3. Correction is performed through table conversion.
FIG. 26 is a block diagram of APPARATUS FOR ADJUSTING HUE, CHROMINANCE, AND LUMINANCE OF A VIDEO SIGNAL USING MATRIX CIRCUITS disclosed in U.S. Pat. No. 5,333,070 and referred to herein as "conventional example 2." In FIG. 26, Q1 denotes a Y/C separation circuit which separates a video signal into a brightness signal Y and a color signal C, Q2 denotes a decode circuit which converts the brightness signal Y and the color signal C into three primary colors R, G and B, Q3, Q4 and Q5 denote matrices of 3-row.times.3-column which perform color correction, Q6 denotes an A/D converter which performs analog/digital conversion of the color-corrected signal, Q7 denotes a frame memory which stores the digitized signal, Q8 denotes a ROM which performs .gamma.-conversion, and Q9 denotes a head of a printer. Q10 is a regulation circuit which regulates the coefficient to the matrix circuit Q4.
The operation of the above-mentioned constitution is explained as follows. The operation of the matrix circuits Q3, Q4 and Q5 of 3-row.times.3-column which perform color correction is closely related to the present invention. The matrix circuit Q3 converts the input signal from the RGB coordinate system to an S.sub.fy coordinate system. The S.sub.fy coordinate system is a coordinate system which includes the skin color axis S, the green color axis f, and the brightness axis Y. When the matrix circuit Q3 is Mn, the matrix Mn on the skin color C1 and the green color C2 can be determined as indicated in the following formula. ##EQU1##
The matrix circuit Q4 performs the color regulation using S.sub.fy coordinate system, and outputs the signal expressed by the S.sub.fy coordinate system. When the matrix of the matrix circuit Q4 is Mh, Mh can be expressed as follows. ##EQU2##
The third row of the matrix Mh is (0 0 1) because the brightness of the achromatic signal is not changed. When the third row of the matrix Mh is (0 0 1), the role of each matrix element is as follows.
Taking into consideration the above-mentioned role, the coefficients of the matrix Mh are determined according to the instruction of the regulation circuit Q10. The matrix circuit Q5 converts the input signal from the S.sub.fy coordinate system to the RGB coordinate system. The matrix used here is the inverse matrix of the matrix Mn. Color regulation by the matrix circuit is performed by successively performing the processes by the matrix circuits Q3, Q4, Q5.
In the above-mentioned method and device for color conversion according to conventional example 1, the pre-processing part R2 judges the magnitude of the input R, G and B signals, and outputs the region selection signal S in a fixed manner. The color conversion parameter memory part R3 outputs the parameter of the triangular prism corresponding to the region selection signal S, and the interpolation operating part R5 receives the parameter to perform interpolation. Thus, the conventional device has a disadvantage that highly accurate color correction can not be performed for the signal which must change the triangular prism to be processed though the magnitudes of the input R, G and B signals are same.
The color can not be accurately converted to the gradation of the R, G and B signals and their color mixture of yellow (Y), magenta (M), cyan (C) and gray (K) irrespective of the magnitude of the R, G and B signals. In addition, in conventional example 1, the input R, G and B signals are separated into the minimum signal L and the differential signals X, Y, and then, added to each other by the limit processing part R6. Thus, the over-flow and under-flow processing must be performed during the addition, resulting in the disadvantage that smooth change in gradation is lost depending on whether or not the processing is performed.
On the other hand, the above-mentioned color correction device in conventional example 2 uses the S.sub.fy coordinate system with a disadvantage that the third row of the matrix can only be used under the fixed condition. At the same time, in conventional example 2, when the brightness of the achromatic signal is changed, the third row of the matrix must be regulated, but no items related to its regulation are disclosed. Conventional example 2 has another disadvantage of doubling the processing load because the coordinate system is converted into another coordinate system, and finally returned to the original coordinate system. Moreover, in conventional example 2, color regulation is performed for the skin color C.sub.1 and green color C.sub.2, causing problems in regulating other colors.
The present invention solves the disadvantages related to the above-mentioned conventional examples, and provides a device and a method for color correction which is capable of separating the achromatic color and the chromatic color, and controlling each color independently.
The present invention also provides a device and a method for color correction which is capable of separating the chromatic color by the hue and gradation, and independently controlling each color.
The present invention further provides a color correction device which is capable of preparing an output table to be controlled, and rapidly performing the proceeding using the prepared output table.
The present invention furthermore provides a color correction application device which is capable of providing an environment for easily correcting and regulating the color by changing the output table.